The only problem I could think of is the actual brand names being displayed although if it's just a showreel I don't see any problem in using any of them but to make sure you should probably just call the company directly explain to them the situation and ask if it is okay to use their products in your showreel.

I have never seen a company knock back free advertising though unless it's putting their product in a bad light which if is the case you might want to change the brand name.